Glassell’s Lugworm

Glassell’s Lugworm, Arenicola glasselli

Glassell’s Lugworm Cast, Arenicola glasselli. Photograph taken during an extreme low tide event on the beach of Loreto Bay, Baja California Sur, June 2024. Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:   Glassell’s Lugworm Arenicola glasselli  (Berkeley and Berkeley, 1939) is a member of the Arenicolidae family of Sandworms. The genus Arenicola is one of four genera in this family, and there are six species in this genus. The name Arenicola means sand dweller.

Morphology:  Glassell’s Lugworms are segmented worms that are similar in appearance to common earthworms. They are bilaterally symmetrical and  divided into an abdomen, a thorax, and a small head. The head lacks eyes or appendages. Along their sides, they have paired, branched, parapodia (unjointed lateral outgrowths), which bear chaetae (bristles). They are reddish brown to blackish in color. Glassell’s Lugworms reach a maximum of 9.0 cm (3.5 inches) in length.

Habitat and Distribution:  Glassell’s Lugworms are a burrowing species, found in sand and mud. A lugworm lives in a U-shaped burrow in sand. The U is made of an L-shaped gallery lined with mucus. At the deep end of the “L” a vertical unlined shaft runs up to the surface. This is a head shaft. At the surface the head shaft is marked by a small round depression.
The tail shaft, 5.1 cm (2.0 inches) to 7.6 cm (3.0 inches) from the head shaft and marked by a highly coiled cast of sand. This coil is often the only sign of this worm’s presence. The lugworm lies in this burrow with its head at the base of the head shaft, swallowing sand from time to time. This makes the columns of sand drop slightly, so there is a periodic sinking of the sand in the saucer-shaped depression. Glassell’s Lugworm is a tropical Eastern Pacific species  that in Mexican waters are found throughout the Gulf of California, and south to Guatemala.  They are absent from the West coast of the Baja Peninsula.

Diet: Glassell’s Lugworms are subsurface deposit feeders, eating detritus.

Predators: Glassell’s Lugworms are a poorly studied and understood species. There is very limited documentation regarding their predators. Other species in this genus are eaten by crabs, hermit crabs, flatfish, gobies, sea stars, and shorebirds.

Reproduction: Glassell’s Lugworms are gonochoric (male or female for life). Reproduction is sexual with swarming behavior. Swarming involves  females producing a pheromone, which attracts and signals  the males to shed sperm which in turn stimulates females to shed eggs. Gametes are spawned through a rupture in the body wall (metanephridia).  After fertilization, most eggs become planktonic; although some are retained in the worm tubes or burrowed in jelly masses attached to the tubes (egg brooders). The fertilized eggs develop into trocophore larva, which later metamorphose into the juvenile, and then adult, stages.

Ecosystem Interactions: Again, Glassell’s Lugworms are a poorly studied and understood species. There is very limited documentation of any parasitic, commensal, or symbiotic relationships.  Other similar species have commensal relationships with pea crabs (Brachyurans), but it has not been documented for this species.

Human Interactions: In some regions lug worms are collected as fish bait. This does not appear to be a widespread practice for this species. Glassell’s Lugworms have a very limited impact on human activities. From a conservation perspective, they have not been evaluated. They are relatively common and fairly widespread in distribution so they should be considered as a species of Least Concern.

Synonyms: None